In time-division duplex (TDD) wireless communication systems, a bi-directional communication path is established between two sites, each of which has a transmitter and receiver, and wherein the two transmitters are synchronized so that only one is transmitting an information signal at any time. A TDD system may includes a central access point device, typically with a transmitter and a receiver. The access point establishes a communication link with one or more peripheral devices located within the range of the central site. The peripheral devices typically are transceivers (single unit transmitter/receivers), each of which has a single transmit/receive antenna, although some radios may have separate antennas for transmission and reception.
TDD systems may operate in an environment which is characterized by the existence of multiple signal paths between the transmitter and receiver due to reflections from objects. This multipath propagation introduces fluctuations in the carrier signal amplitude and phase which can distort information contained in the carrier signal modulation. The distortion may result from the thermal noise susceptibility or phase transitions which are associated with amplitude minima, or from signal spectrum nulls separated from the carrier frequency. The separation is inversely related to the differences in arrival time among the multiple signal paths. When the TDD system operates in a localized area, e.g., within a building or home, the nulls occur at frequencies which are more widely separated from the carrier. However, even the most widely-separated nulls may be significant when the modulation spectrum is determined by a high data rate source of multimedia information.
The use of space diversity enables more robust operation in an environment characterized by multipath propagation. Thus there is a need for a method, access point device (e.g., central site) and peripheral device (e.g., a transportable selective radio device) for providing space diversity in a time division duplex system.